In the telecommunications industry, optical transmission devices permit communication of telecommunication signals over optical fibers. In order to increase the distance that an optical signal may travel, it is necessary to amplify the optical signal at selected points along its transmission path. A device that is becoming more prevalent in amplifying optical signals is known as an optical transmit amplifier. One type of optical transmit amplifier is known as an erbium-doped fiber amplifier (EDFA).
It is necessary to assure that the EDFA amplifies not only the power, but also the modulated optical signals that it receives. That is, an optical signal in which there is no modulated information can reach the EDFA. Also, modulated information in the signal can be lost during EDFA amplification. The EDFA, nevertheless, will amplify this optical signal. The output optical signal, however, will have no meaning or value, because it contains no modulated information. An average power detector will indicate an output signal from the EDFA. However, such a detector cannot determine that the output contains modulated information.
There is a need, consequently, for a method and system that detects the proper operation of an optical transmit amplifier such as an EDFA. Such a method and system is needed that detects not only the presence of an optical output signal, but also that modulation exists in the signal.
There is a further need for a method and system for indicating an optical transmit amplifier fault in the event of either or both a loss of modulation and a loss of optical signal power.